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Probe Noise in Quiescent Plasmas

1968; Physical Society of Japan; Volume: 25; Issue: 6 Linguagem: Inglês

10.1143/jpsj.25.1663

1347-4073

H. Ikezi, Masami Fujiwara, Kazuo Takayama,

Dust and Plasma Wave Phenomena

The probe noise in quiescent plasmas has been studied experimentally. The observing frequency f normalized to the electron plasma frequency f p e is between 10 -3 and 1. In the low frequency range, f / f p e ≪1, the probe noise consists of the shot noise for the electron collecting region of the Langmuir probe, even when the probe potential is higher than the space potential. The shot noise arising from the probe electron current suffers a reduction due to the transit time effect near the electron plasma frequency. In this frequency range the thermal noise is observed instead of the shot noise. Resonant increases of the noise current are found at the sheath-plasma resonance and at the plasma wave resonance frequencies. On the other hand the noise current arising from the probe ion current is smaller than the full shot noise level. The reduction factor for the noise is found to depend on f / f p i , where f p i is the ion plasma frequency. A mechanism for the reduction of the ion shot noise is proposed.